Field of the Invention
The invention relates an encoder including a detecting function of an origin position.
Description of the Related Art
An encoder is currently used as a means for detecting a position and a velocity. An example of the encoder is an incremental encoder. Though a counter accumulates a detecting position of the incremental encoder by relative displacement between a scale and a sensor, the detecting position is lost because the counter is reset just after supplying power. Thus, an operation for detecting an origin position is performed by relative displacement between the scale and the sensor when the power is supplied, and the counter is reset when the origin position is realized by an origin signal. This is origin detection. After origin detection, position detection from the origin position becomes performable.
In encoder disclosed in Japanese Patent Laid-Open No. 2012-103230, a digitized origin signal is output based on an origin detecting signal reflected by a pattern for generating an origin signal and acquired by binarizing an output signal, which changes at a predetermined gradient and are entered into a detector.
However, in Japanese Patent Laid-Open No. 2012-103230, when the origin detecting signal varies on a high voltage side or a low voltage side by a noise, an output phase from a binarizing circuit changes and an origin position may be mistaken.
Additionally, when the configuration of Japanese Patent is applied to a rotary encoder, the origin signal is output two times at different angles relative to a rotation angle of the whole circumference. This is because the configuration of Japanese Patent Laid-Open No. 2012-103230 fails to include a method to judge a pattern boundary facing to an origin pattern that a rotary scale has. When the origin signal is output two times at different angles to determine an initial angle of the rotary angle using the origin signal, the rotary encoder may fail to detect the rotation angle.